The present invention relates to a color photographic light-sensitive material and particularly to a color photographic light-sensitive material wherein the dye formation efficiency in the color development step is high and the increase in sensitivity is obtained.
It is known that, upon color development of a silver halide color photographic material, an oxidized aromatic primary amine type color developing agent reacts with a coupler to form an indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine or like dye, thereby forming color image. In such a system, color reproduction is usually based on a subtractive method, and silver halide emulsions selectively sensitive to blue, green, and red light, respectively, and yellow, magenta, and cyan color image-forming compounds which are in a complementary color relation to the sensitivity of the respective emulsions are employed. For example, acylacetanilide or dibenzoylmethane type couplers are generally used for the formation of a yellow color image, pyrazolone, pyrazolobenzimidazole, cyanoacetophenone and indazolone type couplers are generally used for the formation of magenta color images, and phenolic type couplers (e.g., phenols and naphthols) are generally used for the formation of cyan color images.
Many conventional color-image-forming couplers are 4-equivalent couplers. That is, the development of 4 mols of silver halide as an oxidizing agent is theoretically necessary to form 1 mol of dye through the coupling reaction. On the other hand, 2-equivalent couplers are also known, having an active methylene group substituted with a group eliminatable upon oxidative coupling of the coupler with an oxidation product of an aromatic primary amine developing agent. Such 2-equivalent couplers require the development of only 2 mols of silver halide to form 1 mol of dye. Since 2-equivalent couplers require only one-half the silver halide as compared with conventional 4-equivalent couplers to form a dye, their use enables rapid processing of light-sensitive materials because it allows for a reduction in a thickness of light-sensitive layers, resulting improvement of the photographic properties due to the reduction in film thickness, and results in economic advantages.
Several approaches have thus been suggested to produce 2-equivalent couplers from 5-pyrazolone type couplers, which have primarily been used as magenta-forming couplers. For example, the substitution of the 4-position of a pyrazolone: with a thiocyano group is described in U.S. Pat. Nos. 3,214,437 and 3,253,924; with an acyloxy group is described in U.S. Pat. No. 3,311,476; with an aryloxy group is described in U.S. Pat. No. 3,419,391; with a 2-triazolyl group is described in U.S. Pat. No. 3,617,291; and with a halogen atom is described in U.S. Pat. No. 3,522,052.
However, in using these 4-position substituted pyrazolone couplers, there are disadvantages, e.g., serious color fog may result; the reactivity of the couplers may be unsuitable; the couplers may be chemically so unstable that they are converted to materials incapable of color formation with the lapse of time; or synthesis of the couplers is often difficult.
Also, it has hitherto been known to substitute the 4-position of a 5-pyrazolone with an alkylthio group, an arylthio group, or a heterocyclic ring thio group, as described in U.S. Pat. No. 3,227,554. However, with many of these known thio-substituted pyrazolone compounds, the reactivity with the oxidation product of an aromatic primary amine color developing agent is unsuitable and, further, they are difficult to employ in ordinary color light-sensitive materials due to the strong photographic action of the mercapto compound produced as a result of the coupling reaction. In addition, the chemical stability of these couplers is not generally satisfactory.
Further, recently, a high sensitive color photographic light-sensitive material is highly required. But the color sensitivity obtained from the above-described 2-equivalent magenta couplers is not sufficient to produce highly sensitive color photographic light-sensitive materials. Thus, it has been strongly desired to develop a technique for increasing a sensitivity of a magenta color image-forming layer.
Recently, it has been found that a magenta coupler having an alkylthio coupling-off group possesses an extraordinarily high activity and a high color sensitivity (see Japanese Patent Application No. 136497/78, corresponding to U.S. Ser. No. 91,663, filed on Nov. 5, 1979, now U.S. Pat. No. 4,264,723). However, this is still insufficient for obtaining highly sensitive color photographic light-sensitive materials.